The present invention relates to an internal-combustion engine with predominantly swirl-free air inflow into a shallow combustion space, and, more particularly, to a combustion engine having a centrally arranged injection nozzle with a plurality of spray holes and depressions formed in the piston corresponding to the number of injection jets.
Swiss Patent No. 216,497 discloses a shallow combustion space between the cylinder head and the piston. The piston head is provided with radially extending depressions or recesses for the injection jets of a centrally arranged multi-hole nozzle. The depressions starting from the center of the piston head lead as far as the wall of the recess. Therefore, any wetting of the cylinder wall with the fuel is avoided. The edges of these depressions are made ridge-shaped and therefore impede the expansion of the ignited air/fuel mixture in the circumferential direction of the combustion space.
German Auslegeschrift No. 1,476,075 discloses a piston head having formed-in depressions which extend in the direction of the fuel jets of a centrally arranged multi-hole nozzle into the vicinity of the piston edge and run with relatively flat transition radii into the piston head. However, plane portions are located on the piston head between the depressions. This arrangement is unfavorable in terms of flow.
An object on which the present invention is based is to provide on an internal-combustion engine in which further improvements are attainable in the mixture formation during combustion processes with predominant air distribution, while, in particular, the expansion of the ignited mixture in the circumferential direction of the combustion space is to take place without flow losses.
The foregoing object has been achieved in accordance with the present invention by providing the piston with a shallow piston recess, and depressions are formed in the recess bottom so that they have a corrugated shape in relation to the circumferential direction of the piston recess.
As a result of the unique streamlined contour of the piston recess, the edge zones of the injection jets are at a greater distance from the cylinder head and from the depressions in the recess bottom. Settlement of fuel is thereby avoided, as is settlement of fuel on the cylinder wall and in the piston-ring region. The corrugated shape of the recess bottom ensures low flow losses and prevents flow breakaways.